Provided herein are novel compounds and compositions of matter comprising a nitroxide group-containing cargo (or “nitroxide containing group”) and a mitochondria-targeting group (or “targeting group”). The targeting group is believed, without any intent to be bound, to have the ability to preferentially deliver the composition to mitochondrial, delivering the antioxidant and free-radical scavenging activity of the nitroxide group to cells, including but not limited to an enrichment in mitochondria. These compounds are useful, generally, for their antioxidant, electron scavenging and free-radical scavenging capacity, and, more specifically, for example and without limitation, for their radioprotective and radiomitigative abilities and the prevention as well as mitigation of degenerative diseases.
Oxidative stress in cells typically manifests itself by way of generating reactive oxygen species (“ROS”) and reactive nitrogen species (“RNS”). Specifically, the cellular respiration pathway generates ROS and RNS within the mitochondrial membrane of the cell, see Kelso et al., Selective Targeting of a Redox-active Ubiquinone to Mitochondria within Cells: Antioxidant and Antiapoptotic Properties, J Biol. Chem. 276:4588 (2001). Reactive oxygen species include free radicals, reactive anions containing oxygen atoms, and molecules containing oxygen atoms that can either produce free radicals or are chemically activated by them. Specific examples include superoxide anion, hydroxyl radical, and hydroperoxides. In many disease states, the normal response to ROS and RNS generation is impaired.
Naturally occurring enzymes, such as superoxide dismutase (“SOD”) and catalase salvage ROS and RNS radicals to allow normal metabolic activity to occur. Significant deviations from cell homeostasis, such as hemorrhagic shock, lead to an oxidative stress state, thereby causing “electron leakage” from the mitochondrial membrane. This “electron leakage” produces an excess amount of ROS for which the cell's natural antioxidants cannot compensate. Specifically, SOD cannot accommodate the excess production of ROS associated with hemorrhagic shock which ultimately leads to premature mitochondria dysfunction and cell death via apoptosis, see Kentner et al., Early Antioxidant Therapy with TEMPOL during Hemorrhagic Shock Increases Survival in Rats, J Trauma Inj Infect Crit. Care., 968 (2002).
Cardiolipin (“CL”) is an anionic phospholipid exclusively found in the inner mitochondrial membrane of eukaryotic cells, see Iverson, S. L. and S. Orrenius, The cardiolipin cytochrome C interaction and the mitochondria) regulation of apoptosis, Arch Biochem. 423:37-46 (2003). Under normal conditions, the pro-apoptotic protein cytochrome C is anchored to the mitochondrial inner membrane by binding with CL, see Tuominen, E. K. J., et al. Phospholipid cytochrome C interaction: evidence for the extended lipid anchorage, J Biol. Chem., 277:8822-8826 (2002). The acyl moieties of CL are susceptible to peroxidation by reactive oxygen species. When ROS are generated within mitochondria in excess quantities, cytochrome C bound to CL can function as an oxidase and induces extensive peroxidation of CL in the mitochondrial membrane, see Kagan, V. E. et al., Cytochrome C acts as a cardiolipin oxygenase required, for release of proapoptotic, factors, Nat Chem Biol. 1:223-232 (2005); also Kagan, V. E. et al., Oxidative lipidomics of apoptosis: redox catalytic interactions of cytochrome c with cardiolipin and phosphatidylserine, Free Rad Biol Med. 37:1963-1985 (2005).
The peroxidation of the CL weakens the binding between the CL and cytochrome C, see Shidoji, Y. et al., Loss of molecular interaction between cytochrome C and cardiolipin due to lipid peroxidation, Biochem Biophys Res Comm. 264:343-347 (1999). This leads to the release of the cytochrome C into the mitochondrial intermembrane space, inducing apoptotic cell death. Further, the peroxidation of CL has the effect of opening the mitochondrial permeability transition pore (“MPTP”), see Dolder, M. et al., Mitochondria creatine kinase in contact sites: Interaction with porin and adenine nucleotide translocase, role in permeability transition and sensitivity to oxidative damage, Biol Sign Recept., 10:93-111 (2001); also Imai, H. et al., Protection from inactivation of the adenine nucleotide translocator during hypoglycaemia-induced apoptosis by mitochondria/phospholipid hydroperoxide glutathione peroxidase, Biochem J., 371:799-809 (2003). Accordingly, the mitochondrial membrane swells and releases the cytochrome C into the cytosol. Excess cytochrome C in the cytosol leads to cellular apoptosis, see Iverson, S. L. et al. The cardiolipin-cytochrome C interaction and the mitochondria regulation of apoptosis, Arch Biochem Biophys. 423:37-46 (2003).
Moreover, mitochondrial dysfunction and cell death may ultimately lead to multiple organ failure despite resuscitative efforts or supplemental oxygen supply, see Cairns, C., Rude Unhinging of the Machinery of Life: Metabolic approaches to hemorrhagic Shock, Curr Crit. Care., 7:437 (2001). Accordingly, there is a need in the art for an antioxidant which scavenges escaping electrons and the ROS, thereby reducing oxidative stress. Reduction of oxidative stress delays, even inhibits, physiological conditions that otherwise might occur, such as hypoxia.
Also, there is a need to improve the permeability of antioxidants' penetration of the cellular membrane. One of the limitations of SOD is that it cannot easily penetrate the cell membrane. However, nitroxide radicals, such as TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) and its derivatives, have been shown to penetrate the cell membrane better than SOD. Further, nitroxide radicals like, for example and without limitation, TEMPO prevent the formation of ROS, particularly superoxide, due to their reduction by the mitochondrial electron transport chain to hydroxylamine radical scavengers, see Wipf, P. et al., Mitochondria targeting of selective electron scavengers: synthesis and biological analysis of hemigramicidin-TEMPO conjugates, J Am Chem Soc. 127:12460-12461. Accordingly, selective delivery of TEMPO derivatives may lead to a therapeutically beneficial reduction of ROS and may delay or inhibit cell death due to the reduction of oxidative stress on the cell.
Selective delivery may be accomplished by way of a number of different pathways—e.g., by a biological or chemical moiety having a specific targeting sequence for penetration of the cell membrane, ultimately being taken up by the mitochondrial membrane. Selective delivery of a nitroxide SOD mimic into the mitochondrial membrane has proven difficult. Accordingly, there is a need in the art for effective and selective delivery of antioxidants that specifically target the mitochondria and its membranes as well as inter-membrane space to help reduce the ROS and RNS species. The antioxidants also help prevent cellular and mitochondria apoptotic activity which often results due to increased ROS species, see Kelso et al., Selective Targeting of a Redox-active Ubiquinone to Mitochondria within Cells: Antioxidant and Antiapoptotic Properties, J Biol Chem., 276: 4588 (2001). Examples of mitochondria-targeting antioxidants are described in United States Patent Publication Nos. 20070161573 and 20070161544.
There remains a very real need for a composition and associated methods for delivering cargo of various types to mitochondria. In one embodiment, a composition comprising membrane active peptidyl fragments having a high affinity with the mitochondria linked to cargo is provided. The cargo may be selected from a large group of candidates. There is a need for compositions and methods for effectively treating a condition that is caused by excessive mitochondria production of ROS and RNS in the mitochondrial membrane. There also is a need for compounds that can protect cells and tissues of animals against radiation damage.
The biologic consequences of exposure to ionizing radiation (IR) include genomic instability and cell death (Little J B, Nagasawa H, Pfenning T, et al. Radiation-induced genomic instability: Delayed mutagenic and cytogenetic effects of X rays and alpha particles. Radiat Res 1997; 148:299-307). It is assumed that radiolytically generated radicals are the primary cause of damage from IR. Direct radiolysis of water and the secondary reactive intermediates with a short lifetime (10−10-10−6 seconds) mediate the chemical reactions that trigger the damage of cellular macromolecules, including DNA and proteins, as well as phospholipids in membranes (Mitchell J B, Russo A, Kuppusamy P, et al. Radiation, radicals, and images. Ann N Y Acad Sci 2000; 899:28-43). The DNA is believed to be the primary target for the radical attack, resulting in single and double DNA strand breaks (Bryant P E. Enzymatic restriction of mammalian cell DNA: Evidence for double-strand breaks as potentially lethal lesions. Int J Radiat Biol 1985; 48:55-60). To maintain the genomic integrity, multiple pathways of DNA repair and cell-cycle checkpoint control are activated in response to irradiation-induced DNA damage (Elledge S J. Cell cycle checkpoints: Preventing an identity crisis. Science 1996; 274:1664-1672). Failure of these repair and regulatory systems leads to genotoxicity, malignant transformation, and cell death (Sachs R K, Chen A M, Brenner D J. Proximity effects in the production of chromosome aberrations by ionizing radiation. Int J Radiat Biol 1997; 71:1-19).
One of the major mechanisms of IR-induced cell death is apoptosis, most commonly realized through a mitochondria-dependent intrinsic pathway (Newton K, Strasser A. Ionizing radiation and chemotherapeutic drugs induce apoptosis in lymphocytes in the absence of Fas or FADD/MORT1 signaling. Implications for cancer therapy. J Exp Med 2000; 191:195-200). The latter includes permeabilization of mitochondria followed by the release of cytochrome (cyt) c and other proapoptotic factors (Smac/Diablo [second mitochondrial-derived activator of caspase/direct inhibitor of apoptosis-binding protein with low pI], EndoG [endonuclease G], Omi/HtrA2, and AIF [apoptosisinducing factor]) into the cytosol as the key events in the execution of the death program. The released cyt c facilitates the formation of apoptosomes by interacting with apoptotic protease activating factor 1 (Apaf-1) and then recruits and activates procaspase-9 and triggers the proteolytic cascade that ultimately leads to cell disintegration. Release of proapoptotic factors and caspase activation designate the commencement of irreversible stages of apoptosis. Therefore, significant drug discovery efforts were directed toward the prevention of these events, particularly of the mitochondrial injury representing an important point of no return (Szewczyk A, Wojtczak L. Mitochondria as a pharmacological target. Pharmacol Rev 2002; 54:101-127). However, the exact mechanisms of cyt c release from mitochondria are still poorly understood. It was postulated that generation of reactive oxygen species (ROS), likely by means of disrupted electron transport, has a crucial role in promoting cyt c release from mitochondria (Kowaltowski A J, Castilho R F, Vercesi A E. Opening of the mitochondrial permeability transition pore by uncoupling or inorganic phosphate in the presence of Ca2+ is dependent on mitochondrial-generated reactive oxygen species. FEBS Lett 1996; 378:150-152). Notably, ROS can induce mitochondria membrane permeabilization both in vitro and in vivo, and the mitochondrial membrane transition pore was shown to be redox sensitive (Kroemer G, Reed J C. Mitochondrial control of cell death. Nat Med 2000; 6:513-519).
Conversely, antioxidants and reductants, overexpression of manganese superoxide dismutase (MnSOD) (Wong G H, Elwell J H, Oberley L W, et al. Manganous superoxide dismutase is essential for cellular resistance to cytotoxicity of tumor necrosis factor. Cell 1989; 58:923-931), and thioredoxin (Iwata S, Hori T, Sato N, et al. Adult T cell leukemia (ATL)-derived factor/human thioredoxin prevents apoptosis of lymphoid cells induced by L-cystine and glutathione depletion: Possible involvement of thiol-mediated redox regulation in apoptosis caused by pro-oxidant state. J Immunol 1997; 158:3108-3117) can delay or inhibit apoptosis. Previous studies showed that early in apoptosis, a mitochondria-specific phospholipid-cardiolipin (CL) translocated from the inner to the outer mitochondrial membrane and activated cyt c into a CL-specific peroxidase (Fernandez M G, Troiano L, Moretti L, et al. Early changes in intramitochondrial cardiolipin distribution during apoptosis. Cell Growth Differ 2002; 13:449-455 and Kagan V E, Tyurin V A, Jiang J, et al. Cytochrome c acts as a cardiolipin oxygenase required for release of proapoptotic factors. Nat Chem Biol 2005; 1:223-232). The activated cyt C further catalyzed the oxidation of CL by using mitochondrially generated ROS (Kagan V E, Tyurin V A, Jiang J, et al. Cytochrome c acts as a cardiolipin oxygenase required for release of proapoptotic factors. Nat Chem Biol 2005; 1:223-232). Most importantly, oxidized CL is an important contributor to the release of cyt c from mitochondria (Kagan V E, Tyurin V A, Jiang J, et al. Cytochrome c acts as a cardiolipin oxygenase required for release of proapoptotic factors. Nat Chem Biol 2005; 1:223-232 and Petrosillo G, Casanova G, Matera M, et al. Interaction of peroxidized cardiolipin with rat-heart mitochondrial membranes: Induction of permeability transition and cytochrome c release. FEBS Lett 2006; 580:6311-6316), which might be attributed to changes in microenvironment for the interaction between this phospholipid and cyt C (Ott M, Robertson J D, Gogvadze V, et al. Cytochrome c release from mitochondria proceeds by a two-step process. Proc Natl Acad Sci USA 2002; 99:1259-1263 and Gamido C, Galluzzi L, Brunet M, et al. Mechanisms of cytochrome C release from mitochondria. Cell Death Differ 2006; 13:1423-1433) and/or participation of oxidized CL in the formation of mitochondrial permeability transition pores (MTP) in coordination with Bcl-2 family proteins (Bid, Bax/Bak), as well as adenine nucleotide translocator (ANT) and voltage-dependent anion channel (VDAC) (Petrosillo G, Casanova G, Matera M, et al. Interaction of peroxidized cardiolipin with rat-heart mitochondrial membranes: Induction of permeability transition and cytochrome C release. FEBS Lett 2006; 580:6311-6316 and Gonzalvez F, Gottlieb E. Cardiolipin: Setting the beat of apoptosis. Apoptosis 2007; 12:877-885). In addition to their essential role in the apoptotic signaling pathway, ROS were also implicated in perpetuation of the bystander effect (Narayanan P K, Goodwin E H, Lehnert B E. Alpha particles initiate biological production of superoxide anions and hydrogen peroxide in human cells. Cancer Res 1997; 57:3963-3971 and Iyer R, Lehnert B E. Factors underlying the cell growth-related bystander responses to alpha particles. Cancer Res 2000; 60:1290-1298) and genomic instability after irradiation exposure (Spitz D R, Azzam E I, Li J J, et al. Metabolic oxidation/reduction reactions and cellular responses to ionizing radiation: A unifying concept in stress response biology. Cancer Metastasis Rev 2004; 23:311-322; Limoli C L, Giedzinski E, Morgan W F, et al. Persistent oxidative stress in chromosomally unstable cells. Cancer Res 2003; 63:3107-3111; and Kim GJ, Chandrasekaran K, Morgan W F. Mitochondrial dysfunction, persistently elevated levels of reactive oxygen species and radiation-induced genomic instability: A review. Mutagenesis 2006; 21:361-367). Hence, elimination of intracellular ROS, particularly its major source, mitochondrial ROS, by antioxidants may be an important opportunity for developing radioprotectors and radiomitigators. Protection by antioxidants against IR has been studied for more than 50 years (Weiss J F, Landauer M R. Radioprotection by antioxidants. Ann N Y Acad Sci 2000; 899:44-60).
One of the major mechanisms of ionizing irradiation induced cell death is apoptosis, most commonly realized through a mitochondria dependent intrinsic pathway. Oxidation of cardiolipin catalyzed by cytochrome c, release of cytochrome c and other pro-apoptotic factors into the cytosol and subsequent caspase activation are the key events in the execution of the death program designating the commencement of irreversible stages of apoptosis.
In Belikova, N A, et al., (Cardiolipin-Specific Peroxidase Reactions of Cytochrome C in Mitochondria During Irradiation-Induced Apoptosis, Int. J. Radiation Oncology Biol. Phys 2007, 69(1): 176-186), a small interfering RNA (siRNA) approach was used to engineer HeLa cells with lowered contents of cyt c (14%, HeLa 1.2 cells). Cells were treated by γ-irradiation (in doses of 5-40 Gy). Lipid oxidation was characterized by electrospray ionization mass spectrometry analysis and fluorescence highperformance liquid chromatography-based Amplex Red assay. Release of a proapoptotic factor (cyt c, Smac/DIABLO) was detected by Western blotting. Apoptosis was revealed by caspase-3/7 activation and phosphatidylserine externalization. They showed that irradiation caused selective accumulation of hydroperoxides in cardiolipin (CL) but not in other phospholipids. HeLa 1.2 cells responded by a lower irradiation-induced accumulation of CL oxidation products than parental HeLa cells. Proportionally decreased release of a proapoptotic factor, Smac/DIABLO, was detected in cyt c-deficient cells after irradiation. Caspase-3/7 activation and phosphatidylserine externalization were proportional to the cyt c content in cells. They concluded that cytochrome C is an important catalyst of CL peroxidation, critical to the execution of the apoptotic program. This new role of cyt c in irradiation-induced apoptosis is essential for the development of new radioprotectors and radiosensitizers.
Significant drug discovery efforts have been directed towards prevention of these events, particularly of the mitochondrial injury that represents an important point of no return. Although the exact mechanisms are still not well understood, generation of reactive oxygen species (ROS) and oxidation of cardiolipin by the peroxidase function of cytochrome C/cardiolipin complexes are believed to play a critical role in promoting cytochrome C release from mitochondria. ROS—superoxide radicals dismutating to H2O2—feed the peroxidase cycle and facilitate accumulation of oxidized cardiolipin. Hence, elimination of intracellular ROS, particularly its major source, mitochondrial ROS, by electron and radical scavengers is a promising opportunity for developing radioprotectors and radiomitigators. Significant research has been conducted in the field of radiation protection to use antioxidants against ionizing irradiation (Weiss et al. Radioprotection by Antioxidants. Ann N Y Acad Sci 2000; 899:44-60).
A new class of antioxidants, stable nitroxide radicals, has been suggested as potent radioprotectors due to multiplicity of their direct radical scavenging properties as well as catalytic enzyme-like mechanisms (Saito et al. Two reaction sites of a spin label, TEMPOL with hydroxyl radical. J Pharm Sci 2003; 92:275-280; Mitchell et al. Biologically active metal-independent superoxide dismutase mimics. Biochemistry 1990; 29:2802-2807). TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) is a nitroxide whose properties as a radioprotector in vitro and in vivo have been extensively studied (Mitchell et al. Nitroxides as radiation protectors. Mil Med 2002; 167:49-50; Hahn et al. In vivo radioprotection and effects on blood pressure of the stable free radical nitroxides. Int J Radiat Oncol Biol Phys 1998; 42:839-842. Mitchell et al. Inhibition of oxygen-dependent radiation-induced damage by the nitroxide superoxide dismutase mimic, tempol. Arch Biochem Biophys 1991; 289:62-70; Hahn et al. Tempol, a stable free radical, is a novel murine radiation protector. Cancer Res 1992; 52:1750-1753). Currently, TEMPOL is in clinical trials as a topical radiation protector to prevent hair loss during cancer radiotherapy. While found promising and relatively effective, the required high millimolar concentrations of TEMPOL, mainly due to its poor partitioning into cells and mitochondria, set a limit for its broader applications (Gariboldi et al. Study of in vitro and in vivo effects of the piperidine nitroxide Tempol—a potential new therapeutic agent for gliomas. Eur J Cancer 2003; 39:829-837). In addition, it has been demonstrated that TEMPOL must be present during irradiation to exert its radioprotective effect (Mitchell et al. Radiation, radicals, and images. Ann N Y Acad Sci 2000; 899:28-43; Mitchell et al. Inhibition of oxygen-dependent radiation-induced damage by the nitroxide superoxide dismutase mimic, tempol. Arch Biochem Biophys 1991; 289:62-70), This suggests that the protective mechanisms of TEMPOL are limited to its interactions with short-lived radiolytic intermediates produced by irradiation.
Sufficient concentrations of antioxidants at the sites of free radical generation are critical to optimized protection strategies. A great deal of research has indicated that mitochondria are both the primary source and major target of ROS (Reviewed in Orrenius S. Reactive oxygen species in mitochondria-mediated cell death. Drug Metab Rev 2007; 39:443-455). In fact, mitochondria have been long considered as an important target for drug discovery (Szewczyk et al., Mitochondria as a pharmacological target. 221 Pharmacol. Rev. 54:101-127; 2002; Garber K. Targeting mitochondria emerges as therapeutic strategy. J. Natl. Cancer Inst. 97:1800-1801; 2005).
Chemistry-based approaches to targeting of compounds to mitochondria include the use of proteins and peptides, as well as the attachment of payloads to lipophilic cationic compounds, triphenyl phosphonium phosphate, sulfonylureas, anthracyclines, and other agents with proven or hypothetical affinities for mitochondria (Murphy M P. Targeting bioactive compounds to mitochondria. Trends Biotechnol. 15:326-330; 1997; Dhanasekaran et al., Mitochondria superoxide dismutase mimetic inhibits peroxideinduced oxidative damage and apoptosis: role of mitochondrial superoxide. Free Radic. Biol. Med. 157 39:567-583; 2005; Hoye et al., Targeting Mitochondria. Acc. Chem. Res. 41: 87-97, 2008).